1. Field of the Invention
This invention relates to alginate gels, and, more particularly, to alginate gel systems of propylene glycol alginate and an aluminum salt as the gelling agent.
2. Description of the Prior Art
Alginate has been used for many years as a gelling agent in puddings, fruit fillings, dessert gels, and structured foods, as a water binder in frozen foods, pastry fillings syrups, and icings, as an emulsifier in salad dressings and meat flavor sauces, and as a stabilizer in beer, fruit juice, toppings, sauces and gravies.
Representative of the alginate gel art are the following U.S. Pat. Nos. 2,441,720; 2,918,375; 3,060,032; 3,352,688; 3,770,462; and EP 345886.
Propylene glycol alginates are esters of alginic acid which are commercially available with various degrees of esterification ranging from about 40% to about 90% ester. These alginates are used in such products as salad dressings, and for stabilization of beer foam, where an acid pH is present. However, such alginates have not been considered for gel formation, or for the production of useful gels.
What is described herein is a gel system comprising propylene glycol alginate and an aluminum salt, preferably a sparingly water soluble aluminum salt, and, most preferably basic aluminum acetate.
In a preferred embodiment of the invention, the propylene glycol alginate is esterified in the range 40-90%, and is present in an amount of about 0.5-5.0 wt. %, preferably about 1.0-2.5 wt. %.
In the gel system herein, the aluminum concentration preferably is in the range 20-100% of complete reaction with the carboxyl groups of the alginate, most preferably about 35-75% of complete reaction. A nonionic polymeric viscosifier also may be included therein, particularly if excess aluminum ions are present.
As a feature of the invention, there is provided a process of making such a gel system by adding an aqueous slurry of the aluminum salt to the propylene glycol alginate, suitably at ambient temperature.
A dry blend of the gel system components is provided herein for suitable dispersion in an aqueous media with agitation to form the desired gel system.
Another feature herein is the provision of a formulation including the above-described gel system, such as a personal care formulation.
In this invention, the combination of propylene glycol alginate and an aluminum salt, preferably a sparingly soluble aluminum salt, such as basic aluminum acetate, Al(OH)(C2H3O2)2, provides a useful range of gels, whose characteristics will depend upon the degree of esterification of the alginate and the amount of aluminum salt used. Gel textures ranging from soft and elastic to firm and rigid can be made herein as the components are varied. For example, propylene glycol alginates with a high degree of esterification generally will produce soft, elastic gels while a lower degree of esterification will provide firm, brittle gels.
Advantageously, in this invention, gelation does not occur immediately so that a sequestrant is not needed to slow down the rate of reaction, as in previous alginate gel systems. Actually, the aluminum salt may be added to the alginate in an aqueous medium and the resulting solution filled into a container before gelation occurs. Reaction of the propylene glycol alginate with the sparingly soluble aluminum salt is slowed down herein by the presence of the ester group in the alginate so that some period of time is required to build-up the gel structure. In this manner, a very desirable uniform gel is obtained.
In the preferred forms of the invention, the propylene glycol alginate is esterified to about 40-90%; its concentration in the aqueous gel system is about 0.5-5.0 wt. %, most preferably 1-2.5 wt. %; and the aluminum salt concentration will provide 20-100% of complete reaction with the carboxyl groups of the alginate, most preferably 35-75%.